1. Field of the Invention
The present invention relates to a method for coating a phosphor on a flat display using electrophoretic deposition (EPD) and photolithography, and more particularly, to a method for coating a phosphor on a flat display in which EPD and UV lithography are combined to make a simple and reliable phosphor coated film to thereby enhance an adhesive strength greatly to accordingly heighten stability, and a photoresist is used to make a RGB phosphor pattern for embodying full colors according to the photolithography.
2. Description of Prior Art
A phosphor coating technology is essential in a display or light emitting diode (LED) industrial field. Electrophoretic deposition (EPD) is recently spotlighted among a variety of coating technologies. In particular, the EPD is essential for embodying a flat display such as a FED (Field emission Display) or a PDP (Plasma Display Panel). Phosphor coating technologies, which have been known, will now be described.
Firstly, there is a slurry method. In the case of the slurry method, a phosphor is dispersed uniformly on a photoresist (PR) and then an adding agent such as an interface active agent and a dispersion agent are put in order to make slurry. Then, the slurry is coated on a panel and ultra-violet (UV) cured to make a phosphor film (see Advanced Materials, pp95-97, No. 2, November 1999).
Secondly, there is an electrophotographic method. In the case of the electrophotographic method, a photoconductive layer is formed and exposed via a shadow mask to make a conductive pattern. Then, a phosphor carrying frictional charges is coated thereon (see Advanced Materials, pp97-99, No. 2 November 1999).
Thirdly, there is a settling method. In the case of the settling method, an alkali solution including silicic acid is dispersed in a phosphor. Then, phosphor partilces are settled, dried and coated thereon (Advanced Materials, pp100-101, No. 2, November 1999).
Also, there is an electrophoretic deposition (EPD) method that has been recently noted. Electrophoretic deposition means a phenomenon that electrically charged particles are moved in a suspension by an electrical field. In the case of the EPD, a phosphor is electrically charged by adding a proper amount of an electrolyte in a predetermined suspension, and is biased by an electrical field. Then, surface charged phosphor particles are moved to an electrode of a counter-polarity and coated on the electrode. In this case, nitrocellulose, acryl resin or nitrate groups are used as the additives for enhancing an adhesive strength with respect to a substrate (electrode).
In the case of a transmissive flat display such as a FED, a phosphor density should be smaller than several milligrams per square centimeter (mg/cm2). In the case of the EPD, an electrolyte such as Mg nitrate, La nitrate, Y nitrate is dissolved in IPA (isopropyl alcohol) and then a phosphor is dispersed and biased by an electrical field, to thereby coat the phosphor on a substrate. In this case, an annealing process is performed for one hour at 425xc2x0 C. as a post-process in order to enhance an adhesive strength (see Advanced Materials, pp101-102, No. 2, November 1999).
Besides, there are various methods including a screen printing method and so on.
As described above, there have been known many technologies such as a slurry method, an electrophotographic method, and a settling method as the conventional phosphor coating methods. However, displays manufactured according to the above conventional methods do not satisfy conditions necessary for high-information content displays. Further, most of the displays have been designed to be adapted to displays such as CRTs (Cathode Ray Tubes), which are driven by high electron energy of 10-40 KeV.
However, a next-generation display, e.g. FED is driven at low voltage of 500-1000V. Accordingly, a thin phosphor screen is required. Here, the EPD is used for coating the thin phosphor screen. However, in the case that a phosphor is coated via the EPD, glycerin is added in an electrolyte solution in order to enhance an adhesive strength between the phosphor and a substrate, since the adhesive strength of the phosphor is weak, or an annealing process should be performed for one hour or so at 425xc2x0 C.
To solve the prior art problems, it is an object of the present invention to provide a method for coating a phosphor on a flat display using electrophoretic deposition (EPD) and photolithography, and more particularly, to a method for coating a phosphor on a flat display in which EPD and UV lithography are combined to make a simple and reliable phosphor coated film to thereby enhance an adhesive strength greatly to accordingly heighten stability, and a photoresist is used to make a RGB phosphor pattern for embodying full colors according to the photolithography.
To accomplish the above object of the present invention, according to the present invention, there is provided a method for coating a phosphor on a flat display, the method comprising the steps of: forming a conductive layer on a glass substrate; coating a phosphor on the conductive layer by electrophoretic deposition using a phosphor suspension in which a phosphor to be coated has been dispersed; and forming an adhesive layer by coating a UV curable layer on the upper surface of the substrate, and curing the UV curable layer by irradiating UV light.
According to another aspect of the present invention, there is provided a method for coating a phosphor on a flat display, the method comprising the steps of: (a) forming a conductive layer on a glass substrate; (b) forming a first photoresist layer on the conductive layer, and patterning the first photoresist layer into a desired first pattern, to thereby form a plurality of first windows with respect to the conductive layer; (c) selectively coating a first phosphor on the conductive layer through the plurality of the first windows by electrophoretic deposition using a first phosphor suspension in which a phosphor to be coated has been dispersed, to thereby form a plurality of first phosphor pattern cells; (d) forming a first UV curable layer on the upper surface of a substrate including the coated and exposed first phosphor pattern cells, and selectively curing the first UV curable layer by selectively irradiating UV light to the upper portions of the first phosphor pattern cells, to thereby selectively form a plurality of first adhesive layers in the exposed portions of the first phosphor pattern cells; (e) forming a plurality of second phosphor pattern cells coated with a second phosphor in the position adjacent the first phosphor pattern cells following the step (d), in the same manner as the first phosphor coating method, and selectively forming a plurality of second adhesive layers on the upper portions of the plurality of the second phosphor pattern cells; and (f) forming a plurality of third phosphor pattern cells coated with a third phosphor in the position adjacent the first and second phosphor pattern cells, in the same manner as the first phosphor coating method, and selectively forming a plurality of third adhesive layers on the upper portions of the plurality of the third phosphor pattern cells.
The curable layer is formed by aqueous solution containing polyvinyl alcohol (PVA) and ammonium dichromate (ADC). The aqueous solution can be formed by anyone of spraying, dipping and spin coating methods.
The first through third phosphors are made of red, blue and green phosphors for full color realization, and form a single pixel cell.
Further, it is possible to use aqueous solution containing polyvinyl alcohol (PVA) and ammonium dichromate (ADC) as the photoresist layer.
Also, in the present invention, the phosphor is coated by the EPD and then the phosphor remaining in the phosphor dispersion aqueous solution is evaporated from the aqueous solution for one hour or longer at 100xc2x0 C. or higher. Then, the phosphor is collected in the form of powders via a sonic device, and the collected phosphor can be re-used.
As described above, in the present invention, the EPD and UV lithography are combined to make a simple and reliable phosphor coated film to thereby enhance an adhesive strength greatly to accordingly heighten stability, and a photoresist is used to make a RGB phosphor pattern according to the photolithography, to thereby embody a full color flat display.